Interciencia

ISSN: 0378-1844

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Asociación Interciencia

Venezuela

Moretto, Geraldo

Mortality of varroa destructor in broodless africanized and carnica honey bee (apis mellifera L.)

colonies

Interciencia, vol. 27, núm. 12, diciembre, 2002, pp. 702-704

Asociación Interciencia

Caracas, Venezuela

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702 DEC 2002, VOL. 27 Nº 12

MORTALITY OF Varroa destructor IN BROODLESS AFRICANIZED AND

CARNICA HONEY BEE (Apis mellifera L.) COLONIES

Geraldo Moretto

Introduction

The mite Varroa destructor(Anderson and Trueman,2000), after attacking Apismellifera bees, rapidly dis-persed itself throughout theworld, causing serious lossesto apiculture (De Jong, 1990).

The dispersal of the V. de-structor in various parts of theworld is characterized by dif-ferent population dynamics atlocations where the parasite

became established. The de-gree of infestation varies fromregion to region, with climateand race of A. mellifera beingfactors that affect the develop-ment of the parasite (De Jonget al., 1984; Moretto et al.,1991). Thus, under the condi-tions of Europe and other re-gions of temperate climate themite has hindered the practiceof apiculture without the useof acaricides, while in otherregions of the world a perfect

parasite-host relationship hasbecome established betweenthe mite and the bees (Gon-çalves, 1987).

Among the various races ofA. mellifera bees, Africanizedbees show greater tolerancefor the varroa than bees ofEuropean races. Reproductiveability of female mites isknown to be lower amongAfricanized bees than that ofEuropean bees (Camazine,1986). However, the different

0378-1844/02/12/702-03 $ 3.00/0

KEYWORDS / Africanized Bees / Apis mellifera / Carnica Bees / Varroa Mortality / Varroa destructor /Received: 08/09/2002. Modified: 11/05/2002. Accepted: 11/12/2002

Geraldo Moretto. Biologist. Doctorin Genetics, Universidade Re-gional de Blumenau (FURB).Professor of Genetics, Departa-

reproductive ability of varroaamong different A. melliferasubspecies seems not to be theonly factor responsible for thedifferent virulence of the pest.Hygienic behavior of bee colo-nies is also an important factoracting on the population dy-namics of this parasite (Spivakand Gilliam, 1998; Spivak andReuter, 2001).

Moretto et al. (1993) ob-tained a 40% rate of African-ized bees that were able to rid

mento de Ciências Naturais,FURB. Address: Centro deCiências Exatas e Naturais,Universidade Regional de

SUMMARY

Varroa destructor infestation varies with climate conditionsand race of Apis mellifera bees. Africanized bees show greatertolerance to varroa compared to bees of European races. Repro-ductive ability of female mites, hygienic behavior and groomingbehavior are important factors in population dynamics of thisparasite. The present study shows the mortality rate of the V.destructor mite in Africanized and Carnica bee colonies in

Southern Brazil. The daily proportion of dead and live mitefallen on the bottom of the hive was determined when the totalmite population was of adult bees. In Africanized bee coloniesthe daily proportion of dead mite was 6.30%, while in Carnicabee colonies was 2.11%. The daily proportion of live mite on thebottom of the hive was 2.45% and 0.82% in Africanized andCarnica bee colonies, respectively.

Blumenau, 89.010-971 Blume-nau-SC, Brazil.e-mail: gmoretto@furb.br

RESUMO

Os níveis de infestação alcançados pelo ácaro Varroadestructor variam com as condições climáticas e a raça de abe-lhas Apis mellifera. As abelhas africanizadas apresentam maiortolerância a esse parasita quando comparadas com abelhas dasraças européias. A capacidade reprodutiva, o comportamento higi-ênico e o comportamento de “grooming” são importantes fatoresna dinâmica populacional desse ácaro. O presente trabalho ava-liou a taxa de mortalidade diária do ácaro Varroa destructor em

colônias de abelhas africanizadas e carnicas. A proporção diáriade varroas mortas e vivas encontradas no fundo da colmeia foideterminado em colônias de abelhas contendo apenas operáriasadultas(ausência total de cria). A proporção diária de acarosmortos foi de 6,30% e 2,11%, nas colônias africanizadas ecarnicas, respectivamente. Quanto a proporção de ácaros vivosencontrados no fundo da colmeia, foi de 2,45% nas abelhas afri-canizadas e de 0,82% nas abelhas carnicas.

RESUMEN

El grado de infestación alcanzado por el ácaro Varroa de-structor varía con las condiciones climáticas y la raza de abejasApis mellifera. Las abejas africanizadas presentan mayortolerancia al parásito cuando se comparan con las abejas derazas europeas. La habilidad reproductiva, el comportamientohigiénico y el comportamiento de “grooming” son importantesfactores en la dinámica poblacional del ácaro. El presente trabajohá evaluado la tasa de mortalidad diaria del ácaro V. destructor

en las colonias de abejas africanizadas y cárnicas en el sur deBrasil. La proporción diaria de varroas muertas y vivas en elfondo de las colmenas fue determinada cuando las colmenastenían solamente abejas adultas (colmenas sin crías). Laproporción diaria de ácaros muertos fue 6,3% y 2,11% en lascolonias africanizadas y cárnicas, respectivamente. La proporciónde ácaros vivos encontrados en el fondo de la colmena fue 2,45%en las abejas africanizadas y 0,82% en las cárnicas.

703DEC 2002, VOL. 27 Nº 12

themselves of the parasiteamong 20 colonies of artifi-cially infested Africanizedworker bees. When Europeanand Africanized bees are rearedtogether in the same hive, Eu-ropean bees are found to bemore heavily infested (Gúz-man-Novoa et al., 1996; Mo-retto and Mello, 1999).

Correa-Marques et al.(2000), in a study of mitescollected from the bottom ofAfricanized bee hives, ob-served the occurrence of mu-tilation of various body parts,indicating possible attacks bythe workers. Similar resultswere also obtained with otherA. mellifera subspecies (Biene-field et al., 1999; Zaitoun etal., 2001).

The objective of the presentstudy was to assess the mor-tality rate of the V. destructormite in Africanized andCarnica bee colonies.

Material and Methods

The study was conducted inthe experimental apiary of theDepartment of Natural Sci-ences, Regional University ofBlumenau, Municipality ofBlumenau, Santa Catarinastate, Brazil. The experimentswere conducted using 4 colo-nies with 4 frames covered byAfricanized bees collectedfrom natural swarms in theBlumenau region, and 4 colo-nies (nuclei) of Carnica beeswhose mated queens were im-ported from the experimentalapiary of the University ofTübingen, Germany. WhenCarnica queens were intro-duced in Africanized beecolonies, varroa infestation onadult bees was similar (ap-proximately 2%) to the colo-nies with Africanized queens.Experiments started fivemonths after introduction of

the queens, when the popula-tion consisted exclusively ofCarnica bees.

The daily proportion ofdead and live mites fallen onthe bottom of the hive wasdetermined when the totalmite population was concen-trated on adult bees. Thus,the experiments were carriedout when the 8 bee colonies(4 Africanized and 4 Carnicacolonies) had only adultbees. Colonies containingonly adult workers were ob-tained by imprisoning thequeens in introduction cages.When each colony was fullydevoid of brood, the live anddead mites found on the bot-tom of the hive were counteddaily for 6 consecutive days.To prevent bee contact withthe varroas on the bottom ofthe hive, a Nº 8 mesh netwas placed between the bot-tom and the nest.

After the 6 days of counts,all bee colonies were treatedwith the Bayvarol® acaricideto kill the mites present in thecolonies. As each bee colonyhad only adult bees, only onestripe of the acaricide wasplaced between the combs.Varroas (live and dead) foundon the bottom of the hivewere counted from the firstday after treatment up to thethird consecutive day, whenno mites were detected. Thus,the number of varroas col-lected during the 6 days pre-ceding treatment with Bayva-rol, summed to the number ofvarroas killed by the treat-ment was considered to bethe total varroa population ofeach bee hive during the ex-perimental period. Daily ratesof live varroas fallen on thebottom of the hive and dailymortality rates (only deadvarroas) were determined. Themortality rates and the ratesof fallen live mites were de-termined by dividing the dailynumber of dead and livevarroas collected daily on thebottom of the hive respec-tively by the total number ofvarroas in the hive. Bothdaily percentages were calcu-lated only with actual numberof mites in the colony. In or-der to determine the dailypercentages, the number ofdead and live mites collectedon the previous day was ex-cluded from total population.

The Student test was usedto determine the differencesin mortality rates and in therates of falling live varroas atthe hives of Africanized andCarnica bees.

Results and Discussion

The mean mite populationwas 182 (91-416) varroas incolonies of Africanized beesand 501 (248-1081) varroasin Carnica bee colonies.

Tables I and II show thedaily rates of dead and livemites registered on the bottomof the Africanized andCarnica bee hives. The aver-age daily percentage of deadvarroas detected in the presentstudy was 6.30% in African-ized bee colonies and 2.10%

TABLE IDAILY PERCENTAGES OF LIVE (L) AND DEAD (D) MITES COLLECTED FROM THE

BOTTOM OF AFRICANIZED BEE COLONIES*

Bee ColoniesDay 7 24 4 2

D L D L D L D L

1 4.62 2.10 6.10 3.03 4.83 1.10 13.70 10.802 3.19 1.60 6.69 8.33 2.19 0.73 19.48 2.603 1.12 0.00 16.30 0.00 1.50 2.26 6.67 0.504 10.53 5.50 9.30 0.00 3.13 2.34 9.43 0.005 3.13 0.50 5.13 0.00 8.26 12.48 2.08 2.086 1.86 0.00 5.41 0.00 6.60 2.83 0.00 0.00

Mean 4.08 1.62 8.16 1.89 4.41 3.62 8.56 2.66S. Desviation 3.38 2.09 4.25 3.39 2.64 4.41 7.28 4.13

* Percentage of total number of mites collected in a given colony before and after acaricide treatment.

TABLE IIDAILY PERCENTAGES OF LIVE (L) AND DEAD (D) MITES COLLECTED FROM THE

BOTTOM OF CARNICA BEE COLONIES*

Bee ColoniesDay 31 12 29 18

D L D L D L D L

1 1.94 0.50 4.18 0.60 3.87 0.16 0.69 1.612 1.81 0.50 3.45 0.63 4.33 0.00 2.92 1.253 1.35 0.16 2.29 0.00 0.32 1.21 5.65 0.874 1.08 0.10 1.00 1.00 0.97 1.33 3.60 1.355 1.19 0.50 2.73 1.02 1.00 1.00 2.80 3.746 0.91 0.10 0.69 0.70 1.02 1.39 0.92 0.00

Mean 1.38 0.31 2.39 0.66 1.92 0.85 2.76 1.47S. Desviation 0.41 0.21 1.36 0.37 1.72 0.61 1.83 1.25

* Percentage of total number of mites collected in a given colony before and after acaricide treatment.

704 DEC 2002, VOL. 27 Nº 12

in Carnica bee colonies (t=3.36; P= 0.00) and the aver-age daily percentage of livevarroas found on the bottomof the hives was 2.45% forAfricanized bees and 0.82%for Carnica bees (t= 5.58; P=0.00).

In general, the degree ofinfestation reached by thevarroa parasite is lower inAfricanized bees than in beesof European races (De Jong,et al ., 1984; Gonçalves,1987). The reproductive suc-cess of varroa females inworker brood cells is consid-ered to be an important factorin the population dynamics ofthe mite in different bee races(Camazine, 1986; Medina andMartin, 1999).

However, the different re-productive ability can not bethe unique factor involved inthe different levels of infesta-tion reached by the varroapest. In bees of Europeanraces, under temperate climateconditions, mathematicalmodels have estimated a dailymortality rate of the mite V.destructor of the order 0.2 to0.4% during winter, a periodwith little or no brood presentin bee colonies (Fries et al.,1994; Martin, 1998; Calis etal., 1999; Fries and Pérez-Escala, 2001).The higher mor-tality of V. destructor inAfricanized bee coloniescould act as a limiting factorin the development of thepest. In the present study thedaily mortality and daily pro-portion of live mites found onthe bottom of Africanized beecolonies was about threetimes those found in Carnicabee colonies.

Among the total number ofdead mites found in the tworaces of bees in the presentstudy, a part must have beenrelated to the natural mortal-ity of the varroa. However,the different daily rates ofdead varroas observed for thetwo groups of bees suggestthe presence of mechanismsthat reduce the viability ofthis parasite among African-ized bees. The groomingmechanism first described forApis cerana bees (Peng et al.,1987) and later for A.

mellifera (Boecking andRitter, 1993; Moretto et al.,1993) could be responsible, atleast in part, for the differentmortality rates of V. destruc-tor among Africanized andCarnica bees.

During the total absence ofworker and drone brood thedaily mortality rate of varroaamong Africanized bees wasover 6%. Thus, we may esti-mate that the population ofthe mite could be eliminatedwithin a period of 15 to 20days of absence of brood inbee colonies. In contrast,since the mortality of varroasamong Carnica bees is ap-proximately 2% under thesame conditions, the mitepopulation would be elimi-nated within a period of ap-proximately 50 days. This es-timate could be higher if theliving mites are considered.Although part of these varroascould be able to produce a re-invasion in natural conditions,some of them probably woulddie in a short time.

Under tropical climate con-ditions, as is the case for Bra-zil, there are no prolongedperiods with the absence ofbrood in bee colonies, as ob-served in regions of temperateclimate. However, several pe-riods of low food flow usu-ally occur through the year,due to draught or excess rain,leading to a drastic reductionof brood in bee hives. There-fore, during these periods oflow brood presence, large partof the varroa population isconcentrated on adult bees, afact that possibly reduces themite population to low levels.

The varroa mortality amongCarnica bees detected in thepresent study was at least 20times higher than the mortal-ity detected in European beesunder the climatic conditionsof Europe (Fries et al., 1994;Martin, 1998; Calis et al .1999; Fries and Pérez-Escala,2001). Under tropical climateconditions, the levels of infes-tation reached by the varroapest are usually lower thanthose observed in regions oftemperate climate (Moretto etal., 1991; De Jong and Soa-res, 1999). Thus, the climatic

conditions seem not to beonly related to the reproduc-tion of the varroa parasite, butalso to its mortality.

ACKNOWLEDGMENTS

The author thanks AnneZillikens for providing theCarnica queens, and DenilsonBittencourt and Arnor BublitzFilho for their assistance dur-ing the study.

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